Delphi VCL application layout changes when switching theme
Windows 10 paints the border of a window with a 1 pixel wide line in dark color immediately outside of the client area. In addition, outside of this 1 pixel line it paints a 6 or 7 pixels wide light shadow or optionally fully transparent. (The shadow / no shadow is selectable from Performance
settings.
Most, if not all (I didn't check) styles, paint the border in a more traditional way, with a clearly visible 7 pixels wide border.
Here, an example of Windows 10 (no style):
And here a dark style (Carbon):
Finally also the Light
style
To use the Light
and the Carbon
styles gives a similar looking light and dark layout.